Toothed belts generally comprise a body of elastomeric material, embedded in which are a plurality of longitudinal filiform resistant inserts, also called “cords”, and a plurality of teeth covered by a coating fabric.
Each component of the belt contributes towards increasing the performances in terms of mechanical resistance, to decrease the risk of breakage of the belt and increase the specific transmissible power.
The coating fabric of the belts increases the abrasion resistance and hence protects the working surface of the belt from wear which is due to rubbing between the sides and the slopes of the teeth of the belt and the sides and the bottoms of the grooves of the pulley with which the belt interacts. Moreover, the coating fabric decreases the coefficient of friction on the working surface, reduces deformability of the teeth and above all reinforces the root of the tooth, thereby preventing breakage.
The coating fabric used may be constituted by a single layer or, alternatively, may be a double layer to guarantee increased toughness and rigidity. The coating fabric is normally treated with an adhesive, for example RFL (resorcinol-formaldehyde latex) to increase adherence between the body and the fabric.
Currently, many drive systems use gears or chains rather than toothed belts. However, both gears and chains are complex systems to produce. Moreover, both chains and gears produce more noise and function exclusively with oil lubrication. Furthermore, during operation the chains are subject to increased elongation and therefore replacement with a belt would allow greater precision of the drive.
In addition to these main disadvantages, both the control system with chains and the one with gears are very costly.
For these reasons it would therefore be desirable to be able to replace the chains and gears with toothed belts without having to make any adjustments to the drive system as a whole and therefore in these cases the toothed belt would necessarily have to function with oil or even partly immersed in oil.
Numerous studies have been carried out on toothed belts to verify whether they are capable of operating in direct contact with oil. For example, the U.S. Pat. No. 4,099,422 relates to a toothed belt suitable for use in oil bath and comprising a body in elastomeric material, preferably epichlorohydrin, and a double fabric coating the teeth.
The patent application EP0549401 relates to a toothed belt comprising a body formed of a first layer made of CSM or ACSM and a second layer on the side of the teeth formed of an HNBR matrix covered by a fabric treated with HNBR.
However, none of the prior art toothed belts have a high resistance to wear and generally operation in direct contact with oil facilitates breakage of the belt which therefore has a reduced average life.
Therefore, no toothed belt to be used with oil or partly immersed in oil is capable of withstanding the duration tests established for use in vehicle drive systems.
Replacement of chains and gears in existing systems and, therefore, with the overall dimensions already defined, would make it preferable to use toothed belts having a narrower width with respect to the width of the belts normally used in systems not in direct contact with oil.
Due to the limited extension in width of the belt to be used, it would be more probable for malfunction caused by the overall decrease in modulus, for example poor meshing, to occur.
A possible solution could be the use of a material with a much higher modulus than the one used in the toothed belts currently on the market, to form the resistant inserts of the belts, which define the modulus of the belts almost entirely. For example, resistant inserts made entirely of carbon fibre could be used.
However, this alternative solution causes problems of adhesion between the material forming the resistant insert and the mixture of the body and, moreover, materials with a high modulus generally have a much higher cost than the glass resistant inserts currently used.